<html>
<head>
<script>

function boom()
{
  window.addEventListener("DOMSubtreeModified", function(){}, false);

  var m = document.createElementNS("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul", "menuitem");
  document.body.appendChild(m);
  m.setAttribute("type", "checkbox");
  m.setAttribute("checked", "true");
  m.removeAttribute("type");
}

</script>
</head>

<body onload="boom();"></body>
</html>
